FIG. 7 illustrates a semiconductor device with improved heat releasing capability in the prior art. Of leads shown, at least a part of an inner lead 501 is pasted with a nonconductive tape 502 to a heat-releasing block 504 comprising a metallic or other type of material. A semiconductor element 503 is pasted with an epoxy resin not shown in the illustration onto the heat-releasing block 504. The electrode on the semiconductor element 503 and the inner lead 501 is connected with a wire 505 such as a gold wire or the like. These components are sealed with a sealing resin 506, and an outer lead 507 is extracted from the sealing resin 506.
Note here that the general practice is to extract the outer lead 507 from the midpoint of the thickness of the sealing resin 506.
According to the above description, since the heat-releasing block 504 is locate off-centered to one side (i.e. lower side in the illustration) of the sealing resin 506 as seen from its thickness-wise direction, the flow of the sealing resin above and underneath become irregular at the time of resin sealing, thus causing defects such as an unfilled portion. In other words, difference between the spaces above and under the heat-releasing block 504 to the metal forming mold causes a variance in filling speed at the time the sealing resin is injected, delaying the filling of the lower metal forming mold and thus causing a faulty filling. Such a faulty fill is apt to occur particularly when a large and thick heat-releasing block is employed to improve the heat-releasing capability.
While the above-mentioned problem could be solved by making the heat-releasing block thinner, it gives rise to another problem whereby a thinner heat-releasing block could only provide an inferior heat-releasing capability. For instance, for a 3-mm package of a semiconductor device, a heat-releasing plate having a thickness of about 0.5 mm has caused a faulty fill. If a heat-releasing plate of about 1.5 mm in thickness is used to avoid the trouble, heat-releasing capability may be insufficient.
Accordingly, with an aim at eliminating the above-described problems in the prior art, it is an object of the present invention to provide a semiconductor device in which defective resin filling can be prevented and a process for fabricating the same.